1. Field of the Invention
The present invention relates to a remaining-liquid-amount display apparatus and a remaining-liquid-amount display method for displaying the amount of conductive liquid remaining in a liquid container. The present invention is applied to, for example, a case where the amount of ink remaining in an inkjet printer is detected and displayed.
2. Description of the Related Art
In inkjet printers, ink contained in an ink tank is supplied to an ink-discharge unit through an ink flow path, and ink droplets are discharged from the ink-discharge unit.
In addition, in inkjet printers, it is necessary to detect the presence/absence of the ink with relatively high accuracy. The reasons for this will be described below. Firstly, it is difficult to determine the amount of remaining ink by observing the ink tank from the outside.
Secondary, if an ink-discharge operation is continued until the ink is completely consumed, there is a risk that the ink-discharge unit will be damaged. As an example of an ink-discharging method used in inkjet printers, a thermal method in which ink contained in ink cells is quickly heated by exothermic elements to discharge ink droplets is known in the art. In this method, there is a risk that the exothermic elements will be damaged if they are heated when there is no ink in the ink cells. Accordingly, the ink-discharge operation (print operation) must be stopped when the amount of remaining ink is reduced to a predetermined level.
Thirdly, in the case of printing on a large sheet of paper, there is a risk that the ink will run out in the middle of the print operation if the amount of remaining ink cannot be detected with high accuracy, and a partially-printed paper sheet will be wasted in such a case.
Accordingly, in view of safety and economic efficiency, it is necessary to detect the amount of remaining ink with high accuracy.
FIG. 2 is an exploded perspective view showing a first example of a known remaining-ink-amount detector (Japanese Unexamined Patent Application Publication No. 5-201019).
In this example, an ink cartridge a includes elastic ink bags b, and the ink bags b are pushed by compression springs c. In addition, strips d move as the amount of ink decreases, so that the amount of remaining ink can be determined by observing the displacement of the strips d through a window e. Accordingly, the amount of remaining ink can be easily detected at low cost.
FIG. 3 is a block diagram showing a second example of a known ink-remaining-amount detector (Japanese Unexamined Patent Application Publication No. 9-169118).
In this example, the amount of remaining ink is calculated on the basis of an initial amount of ink contained in a tank and the number of times an ink droplet has been discharged. An ink-discharge-amount calculator f includes a counter which counts the number of times an ink-discharge operation has been performed and a multiplier which multiplies the count by the amount of ink discharged in a single ink-discharge operation (average volume). Then, the thus obtained value is transmitted to an ink-remaining-amount calculator g as the amount of ink consumed. The ink-remaining-amount calculator g calculates the amount of remaining ink by subtracting the value calculated by the ink-discharge-amount calculator f from the initial amount of ink contained in the tank.
FIG. 4 is a sectional side view showing a third example of a known ink-remaining-amount detector (Japanese Unexamined Patent Application Publication No. 6-226990).
In this example, a pair of electrodes i are disposed at a position close to the bottom surface of an ink cell h, and the presence/absence of ink is detected on the basis of the resistance between the electrodes i.
FIG. 5 is a sectional side view showing a fourth example of a known ink-remaining-amount detector (Japanese Unexamined Patent Application Publication No. 2000-43287).
In this example, an optical sensor is provided which includes light-reflecting members k1 and k2 disposed on the bottom surface of an ink tank j, light-emitting members m1 and m2 which emit light toward the light-reflecting members k1 and k2, respectively, and light-receiving members n1 and n2 which receive the light emitted from the light-emitting members m1 and m2 and reflected by the light-reflecting members k1 and k2, respectively, and the presence/absence of ink is detected on the basis of the manner in which light is received by the light-receiving members n1 and n2 of the optical sensor.
However, the above-described known techniques have the following problems.
That is, the first example in which the amount of remaining ink is determined by visual observation does not comply with the requirements of recent, high-quality inkjet printers. In addition, when the amount of remaining ink is to be shown on a display or the like, mechanical displacements must be converted into electrical signals, which means that a complex structure is required and high costs are incurred.
In addition, in the second example, the amount of ink consumed is calculated by multiplying the average volume of an ink droplet which is discharged in a single ink-discharge operation by the number of times the ink-discharge operation has been performed. However, if, for example, the ink tank has a large capacity, the difference between the actual volume of an ink droplet discharged and the average volume of an ink droplet which is set in advance gradually increases. Therefore, in view of safety, it is necessary to display a message indicating that the ink has run out while a relatively large amount of ink may still remain. Accordingly, the message indicating that the ink has run out must be displayed while an amount of ink sufficient to continue printing is still contained, and the therefore, remaining ink is wasted.
In addition, in the third example, since only the presence/absence of the ink is detected, the amount of remaining ink cannot be determined. Therefore, there may be a case in which the message indicating that the ink has run out is suddenly displayed and the print operation stops. In such a case, the printer cannot be used afterwards unless a spare ink cartridge is available.
The fourth example also has a problem similar to that of the third example. In addition, in the fourth example, the above-described optical sensor for detecting the amount of remaining ink and the method in which the number of times an ink droplet has been discharged is counted are used in combination, so that the accuracy is improved compared to the second example and the problem of the third example, that is, the message indicating that the ink has been run out is suddenly displayed, can be avoided. However, since it is necessary to use the above-described two methods in combination for detecting the amount of remaining ink, the system becomes complex and high costs are incurred.